The Solomon Islands Opposition is confident that a criminal police investigation now underway against the PM Danny Philip will reveal corruption.

Police say the nature of the complaint being investigated is to see how the Republic of China (Taiwan) funded Prime Minister's discretionary fund has been distributed and by whom.

The Opposition alleges that the Prime Minister may have abused his official position in relation to apportionment of public funds to his family members and associates.

The deputy opposition leader, Matthew Wale, says that the Leadership Code Commission is also investigating.

He says the opposition can prove the PM made payments to people related to him out of this fund

"The total discretionary fund is 10 million Solomon's dollars. And he has used roughly about 7 million of that discretion (fund). Now that 10 million fund was actually allocated to rural solar electrification."

Matthew Wale says investigations into the PM begins the same week the Danny Philip is expected to face a proposed no confidence vote on Friday.